Methyl glucoside (MeG) is an industrial chemical used in the manufacture of various products, including, for example, cosmetics; polyurethane foams; polyether polyols; and etherified or esterified surfactants. MeG also is used as a plasticizer for phenolic, amine, and alkyd resins, in the manufacture of tar-oil varnishes, and for many other industrial purposes. The two isomers of MeG are .alpha.-MeG and .beta.-MeG. Both isomers are commercially useful, as are mixtures of .alpha.- and .beta.-MeG.
MeG may be prepared by reacting starch with methanol in the presence of a catalytic amount of p-toluene sulfonic acid at elevated temperature and pressure. The starch-methanol reaction produces a mixture of products, which mixture includes .alpha.-MeG and .beta.-MeG as predominant species. The methanol can be evaporated and exchanged with water to yield a dark, aqueous solution containing .alpha.-MeG and .beta.-MeG in a ratio ranging from about 1.5:1 to 2.5:1 (.alpha.-MeG:.beta.-MeG). MeG also may be prepared in a similar glucose-methanol reaction.
The dark color of the solution may interfere with the commercial utilization of the MeG solution, for example, in the manufacture of cosmetics or other personal care products. Accordingly, it is known to decolorize the MeG with a bleaching or whitening agent, such as sodium hypochlorite or sodium borohydride. While such whitening agents are effective in decolorizing the MeG solution, their use may leave undesired residual salts, such as sodium and chloride salts, in the MeG solution. Ionic species such sodium and chloride are undesirable in many commercial applications, such as in the manufacture of polyols for polyurethane foams.
A significant drawback of known methods of decolorizing MeG is that dextrose may remain in the MeG solution, even after decolorization. Dextrose is a natural by-product of the reaction used to prepare MeG. Dextrose will caramelize at high temperature, forming a tannish-brown product. Dextrose also will also discolor under conditions of elevated pH. Thus, although a solution of MeG that has been decolorized with a whitening agent may initially have satisfactory color properties, the color of the MeG solution may degrade upon processing under certain reaction conditions.
It is also known to decolorize .alpha.-MeG by crystallizing and separating the .alpha.-MeG from solution. This method is expensive and time-consuming, however, and may reduce the yield of .alpha.-MeG. Moreover, crystallization of .alpha.-MeG may trap impurities within the MeG crystals.
It is a general object of the invention to provide a process for decolorizing a solution of MeG that contains one or more color components and dextrose and optionally, one or more other simple sugar components, to thereby yield a decolorized, low-dextrose MeG solution.